1. Field of the Invention
The present invention relates to mobile communication terminals, and in particular, to a device and method for monitoring the remaining capacity of a battery within the mobile communication terminal.
2. Description of the Related Art
FIG. 1 shows a conventional battery monitoring device for a mobile communication terminal such as a cellular telephone. Referring to FIG. 1, an output voltage of a battery 50 is applied to an analog-to-digital converter (ADC) 20 via a multiplexer (Miux) 30. The ADC 20 converts the input voltage signal to a digital signal. A microprocessor 10 compares the digital signal output from the ADC 20 with a stored threshold value and displays a "LOW BATTERY" state on a display 60 if the digital signal has a level lower than the threshold value. In addition, a voltage characteristic of battery 50 depends on the ambient temperature. Thus, to accurately monitor the battery, the device includes a temperature sensor 40 for sensing temperature of the mobile communication terminal. Multiplexer 30 multiplexes the signals input from the temperature sensor 40 and the battery 50 in response to a control signal output from the microprocessor 10. The microprocessor 10 controls the overall operations of the mobile communication terminal according to the control program in a memory with the threshold value.
In general, the mobile communication terminal has a sleep mode, an idle mode, and a traffic mode, each mode having different current consumption. FIG. 2 shows the voltage characteristics of the battery 50 with respect to the lapse of time. In the drawing, reference numeral 1 denotes a curve illustrating the current consumption (or the discharge time) while in the traffic mode, reference numeral 2 a curve illustrating the current consumption while in the idle mode, and reference numeral 3 a curve illustrating the current consumption while in the sleep mode.
In view of the different current consumption characteristics based on operational modes, the battery 50 may be in a "LOW BATTERY" state during the traffic mode, even though it is not in the "LOW BATTERY" state during the idle mode or the sleep mode. Hence, the user of the mobile communication terminal can not predict the "LOW BATTERY" state well enough in advance, and as such, they may not have enough time to replace the battery with a new one or recharge the existing battery.